1. Field
The present disclosure relates generally to aircraft and, in particular, to aircraft engines. Still more particularly, the present disclosure relates to a method and apparatus for a bearing housing in an engine having stress and stiffness control capabilities.
2. Background
Aircraft may fly using many types of engines. For example, many commercial aircraft use turbo fan engines. A turbo fan engine has a ducted fan, which is powered by a gas turbine. The airstream passes through the gas turbine and through the fan duct to generate thrust. The fan blades in the ducted fan accelerate the air in a manner similar to a propeller. Some of the air passes through the gas turbine providing oxygen to burn fuel. The thrust produced by the turbo fan engine is typically a combination of around 85 percent of thrust generated by the fan and around 15 percent of thrust generated by the exhaust from the engine core.
Turbo fan engines have a number of different configurations. One configuration is a dual shaft turbo fan engine. This type of configuration has a fan and a low pressure compressor together with a low pressure turbine on a low pressure shaft and a high pressure compressor driven by a high pressure turbine on a high pressure shaft. The high pressure shaft may also be an engine core shaft.
The high pressure compressor of the turbo fan engine has several axial stages. These stages are assembled to form the forward part of the high pressure shaft of the engine. The high pressure shaft is supported at the front of the shaft by an assembly of bearings. For larger turbo fans, the forward assembly of bearings for the high pressure shaft is formed by a ball or thrust bearing and a roller or radial bearing. Typically, the outer races of these bearings are integrated into a bearing housing.
Further, the high pressure shaft of the engine is a rotating shaft. The rotating high pressure shaft is assembled to have a rotating balance within a selected amount of tolerance. This balance minimizes the amount of vibration that may occur due to rotation of the shaft during operation of the engine.
Over time, wear and tear on the blades and other portions of the shaft may result in the shaft becoming unbalanced or having a balance level that is out of a desired amount of tolerance. This change in balance will increase the amount of vibration. The amplitude and/or frequency of these vibrations may increase in a manner that may require shutting down the engine during flight and/or performing maintenance on the engine.
These types of vibrations may increase the stress and forces on other components in the engine. These vibrations may decrease the intervals at which maintenance on the engine is needed. With increased maintenance, the expense of maintaining an aircraft may increase. Further, with increased maintenance, the amount of time during which an aircraft is unavailable for use also increases.
Therefore, it would be advantageous to have a method and apparatus that takes into account one or more of these issues, as well as possibly other issues.